A curvilinear rolling guide unit guides its slider which curvilinearly moves along its curvilinear guide rail via rolling elements, and has been used, in recent years, in sliding sections which perform a relative motion in machine tools, transport apparatus, industrial robots, transfer machines, assembling apparatus, semiconductor fabrication systems, etc. Conventionally, many curvilinear rolling guide units have been proposed, but have not yet been sufficiently commercialized.
The applicant of the present application developed a curvilinear rolling guide unit and filed a patent application for the curvilinear rolling guide unit (see, for example, Japanese Patent Application Laid-Open No. 2001-241437). In the curvilinear rolling guide unit, the slider which slides on the guide rail extending curvilinearly with a fixed curvature has a balanced structure and has a reduced size. Also, the curvilinear rolling guide unit allows application of end caps of the same design specifications thereto according to the design specifications of the slider. Even when the length of a carriage of the slider varies, the opposite end surfaces of the carriage are always contained in respective vertical planes which pass the center of curvature of the guide rail and vertically section the guide rail. Common design specifications can be imparted to end caps each having turnaround passages. Since rectilinear return passages are shifted inward of the carriage, the carriage does not have portions which are excessively thick in the radial direction of the guide rail, and the carriage can have a structure which is well balanced in the radial direction and is reduced in size.
Japanese Patent Application Laid-Open No. H08-21441 discloses a curvilinear motion guide device which can be assembled easily and accurately, exhibits high rigidity, and can provide an accurate, infinite curvilinear guide. In the curvilinear motion guide device, moving blocks are mounted on an endlessly formed endless annular guide rail through a large number of rolling elements. In order to mount each moving block on a portion of the endless guide rail, the guide rail is cut at a certain position to form a cut portion, and the end surfaces of the guide rail at the cut portion are shifted from each other, whereby the moving block can be attached to or detached from the guide rail through the cut portion of the guide rail.
Japanese Patent Application Laid-Open No. 2005-257036 discloses a stud type track roller having a lubrication plug. The lubrication plug can be easily attached to lubrication holes of existing stud type track rollers with almost no need to change design, can easily and reliably re-supply lubricant, is compact and easy to manufacture, and is of low cost. In the lubrication plug, a cylindrical large-diameter portion and a cylindrical small-diameter portion to be fitted into a lubrication hole of a stud are formed integrally with each other, and the large-diameter portion and the small-diameter portion have an injection hole extending along an axis and allowing insertion of a lubrication nozzle from the large-diameter portion into the small-diameter portion. An inner surface of the lubrication plug is tapered according to the shape of a grease gun to be used for lubrication so as to establish close contact between the inner surface of the lubrication plug and the outer surface of a tip of the grease gun for prevention of leakage during supply of lubricant.
Japanese Utility Model Application Laid-Open No. H06-58234 discloses a rectilinear motion guide unit whose end seal has a lubricant injection hole formed therein. In the rectilinear motion guide unit, a lubricant injector is inserted into the lubricant injection hole of the end seal, and lubricant is injected through the lubricant injection hole. After completion of lubrication, the lubricant injector is removed from the end seal; as a result, the lubricant injection hole in the form of a pore closes, thereby preventing leakage of grease.
Conventionally, since a curvilinear rolling guide unit is such that a guide rail extends endlessly with a fixed curvature, or in an irregularly curved form, the structure of a slider used in a conventional rectilinear rolling guide unit cannot be applied to the curvilinear rolling guide unit. Specifically, in the conventional curvilinear rolling guide unit, the slider cannot have a structure which is well balanced and is reduced in size, for the following reasons: load-carrying races extend curvilinearly similar to the guide rail, and, in order to allow formation of return passages, the slider must have wasteful wall thickness on the radially inner and outer sides thereof. Also, in the curvilinear rolling guide unit, preparation of end caps of different design specifications in accordance with a change in the curvature of the guide rail or a change in the overall length of the slider results in an increase in the number of components and complication of management. Thus, a problem has been how to provide a curvilinear rolling guide unit in which a slider slides on a guide rail extending curvilinearly with a fixed curvature with a structure which is well balanced and is reduced in size; which allows use of end caps of the same design specifications even when the curvature of the guide rail and the overall length of the slider are changed; and which enables simple management of components.
According to a conventional curvilinear rolling guide unit, if a guide rail of endless type is employed, a slider cannot be mounted on the guide rail. Specifically, the slider is generally composed of a carriage, end caps attached to the opposite ends of the carriage, and end seals attached to end surfaces of the end caps. The carriage is formed of an upper portion and a pair of wing portions extending downward from opposite side portions of the upper portion, and a recess having a width equal to or greater than that of the guide rail is formed between the wing portions; thus, the carriage can straddle the guide rail to thereby be mounted thereon. In contrast, although the end cap is formed of an upper portion and a pair of wing portions extending downward from opposite side portions of the upper portion, since the wing portions have respective scooping portions having scooping beaks extending inward for guiding rolling elements which roll from load-carrying races to respective turnaround passages, the width between the scooping portions is narrower than the width of the guide rail; as a result, the end cap cannot straddle the guide rail as it is. Thus, as disclosed in the above Japanese Patent Application Laid-Open No. 2001-241437, the end cap has a slit which extends from a lubrication hole formed in its upper portion at the center to the under surface thereof. The end cap is elastically deformed at a thin wall portion located above the lubrication hole by external force so as to expand the width between the wing portions, whereby the end cap can straddle the guide rail to thereby be mounted thereon. However, the following problem has been found. When lubricant is supplied to the slider by use of a lubricator in such a manner that the nozzle of the lubricator is inserted into the lubrication hole of the end cap, lubricant leaks through the slit extending from the lubrication hole.